U.S. Pat. No. 6,601,618 and European patent application No. EP 1 101 998 both disclose a filling valve having a hollow valve rod slidingly mounted in a valve housing. The valve rod is provided with a through hole defining a gas passage, and a liquid passage is defined between the outer periphery of the valve rod and the inner periphery of the housing. A diaphragm connects the valve rod to the housing in order to isolate the liquid chamber and a pressure chamber provided to control the vertical position of the valve rod.
In normal operational conditions, such a structure is somewhat satisfactory. However, as soon as the diaphragm breaks, or even if a small leakage occurs at the level of the diaphragm, the liquid can contaminate the pressure chamber, thereby resulting in improper operation of the filling valve. The filling machine must be stopped until the proper maintenance is achieved. This causes losses of productivity.